For their large capacity per unit volume and unit mass, lithium-ion secondary batteries are widely used for laptops and electronic terminals such as mobile phones. Recently, lithium-ion secondary batteries are also applied in electric vehicles which can travel by only a battery, hybrid vehicles which use both a battery and an engine, electric motorcycles, and the like. Moreover, in accordance with the spread of renewable energy and rising awareness of the environment, lithium-ion secondary batteries are also used for stationary batteries, and development in lithium-ion secondary batteries for a large-capacity power storage system and the like become active as well.
Since lithium-ion secondary batteries are used in a potential range in which water cannot exist stably, an electrolytic solution having a non-aqueous organic matter as a main body is used. If moisture is included in a member configuring a lithium-ion secondary battery, the moisture is decomposed at the time of the first charging, and there are cases where hydrogen and oxygen are generated. In such a case, due to the generated hydrogen and oxygen, each of members configuring the lithium-ion secondary battery deteriorates, and the characteristics of the lithium-ion secondary battery are degraded.
Therefore, in a step of manufacturing a lithium-ion secondary battery, main members are sufficiently dried such that no moisture is adsorbed thereto. In addition, lithium-ion secondary batteries are assembled in a dry room from which atmospheric moisture is maximally eliminated (for example, having a dew point equal to or lower than −40° C.).
In this manner, in order to minimize the quantity of moisture included in a lithium-ion secondary battery, the quantity of moisture in members used in a battery is required to be managed strictly.
As a method of measuring the quantity of moisture in such members, there is the Karl Fischer's moisture quantity determination method. In the Karl Fischer's moisture quantity determination method, for example, the amperage flowing in accordance with the chemical reaction below is precisely monitored and the quantity of moisture included in a member is measured.B.I2+B.SO2+B+H2O→2BH+I−+B.SO3 B.SO3+ROH→BH+ROSO3−
In a case where the quantity of moisture in a member is measured, a vaporization apparatus is used for sufficiently heating the member and vaporizing moisture from the member. Examples of such a vaporization apparatus include a type in which a measurement sample is put in a boat and is measured, and a type in which a measurement sample is put in a vial bottle and is measured. In an apparatus of the type in which a measurement sample is put in a boat and is measured, there is a need to perform an operation of switching the sample after a measurement. In contrast, in a vial bottle-type apparatus, measurements can be performed by automatically replacing the sample. Therefore, the quantity of moisture in a member can be efficiently measured by using the vial bottle-type apparatus.
Examples of a technology related to such a vial bottle-type apparatus include technologies disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. H7-43371) and Patent Document 2 (Japanese Unexamined Patent Publication No. H7-43268).
The apparatuses disclosed in those Patent Documents include a turntable, a mechanism for switching a vial bottle, and a mechanism for lifting and lowering the vial bottle. In addition, the apparatuses include a mechanism for selecting a vial bottle having a measurement sample therein, inserting the selected vial bottle into a set heater unit, and heating the vial bottle to a set temperature.
In such apparatuses, inert gas is introduced to the inside of the selected vial bottle, moisture vaporized from the measurement sample is sent to the inside of a Karl Fischer moisture meter together with the inert gas, and the quantity of moisture included in the inert gas is measured. Accordingly, the quantity of moisture in the measurement sample can be determined. In these apparatuses, as long as the measurement sample can be inserted into the vial bottle, it is possible to measure moldings, powder, liquid, and the like unless a substance hindering Karl Fischer reaction is generated.
Generally, the apparatuses disclosed in those Patent Documents manage the quantity of moisture in a member such as an electrode and a separator of a lithium-ion secondary battery.